Announcement

The first issue of 1997 brings two changes. First, we are pleased to announce a further increase in size. Pressure of excellent quality manuscript submissions continues to grow, and this year sees a modest increase in size with each issue around 256 pages. With an earlier increase from four to six issues per year, this represents 40% growth in the total size of each volume in the last 3 years. We recognize the importance of keeping publication delays short, and also the importance of maintaining high quality. The new increase in pages will allow only a modest increase in our current acceptance rate, without loss of these ideals, and the annual volume size is now substantial. Secondly, we adopt structured abstracts with this issue. This format has become widespread in the last few years. It is better suited to the electronic databases, which are essential for the modern scientist and scholar, and to the various forms of electronic publishing, which are supplementing, but not supplanting, the printed page. We are proud of the literary style of our authors and we hope that the structured format can still accommodate it.

The allele in each column is the one associated with 8765delAG for phased genotypes; two alleles are shown for unphased genotypes. Markers not typed because of insufficient DNA are indicated by a dash (-). The physical distance from D13S260 to D13S171 is about 1 Mb; BRCA2 is located between D13S1697 and D13S1701 [2]. The intermarker distances are D13S260 -1.0 cM -D13S1699 -0.7 cM -D13S1698 -0.6 cM -D13S1697 -0.2 cM -BRCA2 -0.5 cM -D13S1701 -0.6 cM -D13S171 [10]. 2 Families PG1940, VN54, 739, 616, 825, 854, 853, W10083, SO28, HD13 and HD86 and the genotypes for markers D13S260, D13S1699, D13S1698 and D13S171 were previously reported [8]. 3 DNA samples from two of the three previously described Yemenite Jewish families harboring 8765delAG [11] were available for genotyping. regard to family history of breast or ovarian cancer [11]. It was the second most common mutation found in 11 out of 97 French Canadian hereditary breast and ovarian cancer families (at least 3 cases of breast or ovarian cancer, and 2 affected individuals were related to the index case as third-degree relatives or closer) [8]. The proportion of French Canadian women who carried 8765delAG and were ascertained without regard to family history of cancer was 2 out of 113 women with ovarian cancer [9] and 2 out of 128 women with breast cancer [Foulkes, W.D. and Tonin, P.T., unpubl. data]. Haplotype analysis using two or five microsatellite markers flanking BRCA2 suggested that 8765delAG was a founder mutation in each of the populations [10,11]. Here, we extend the haplotype anal-ysis to include additional markers, and compare the segregating BRCA2 haplotype in families from these two ethnically and geographically distinct populations.
Seventeen Canadian families of French descent and two Yemenite Jewish families harboring the BRCA2 8765delAG mutation were genotyped for six microsatellite markers flanking BRCA2 and two intragenic singlenucleotide polymorphisms (   - tréal. Mutation carriers and, where available, additional family members were genotyped to determine phase as previously described [8]. We also genotyped two SNPs, IVS8+56C1T and IVS16-14T1C, located in introns 8 and 16 of BRCA2, respectively, by DNA sequencing and allele-specific oligonucleotide hybridization (details available from authors). These SNPs were previously described as sequence variants at nucleotides 909+56 and 8034-14, respectively [12]. The disease-associated haplotype was deduced by inspection of segregating genotypes in the families.
The most common haplotype that segregated with 8765delAG in the French Canadian breast cancer families was 4-3-11-2-C-C-4-9 (table 1). In two families (SO28 and HD86), the disease-associated haplotype was inferred to be recombinant for one of the most distal flanking markers, D13S260 or D13S171. Where phasing was not possible, the disease-associated allele was present. Thus, we infer that the disease-associated haplotype (3-11-2-C-C-4), comprised of four microsatellite markers and two intragenic SNPs, is identical in state in the French Canadian families. In order to estimate marker allele frequencies in the general French Canadian population, we genotyped French Canadian women who were affected with breast cancer, but were not carriers of 8765delAG. Due to limited amounts of DNA, we were not able to genotype a sufficiently large number of samples for the same set of markers in order to estimate haplotype frequencies that take into account linkage disequilibrium. However, the most common allele for five of the eight markers in this sample of 'normal' chromosomes was not the allele associated with 8765delAG (table 2). Under the assumption of linkage equilibrium, the six-marker haplotype is expected to occur less than 1% of the time. This suggests that 8765delAG is carried on an uncommon haplotype in the French Canadian population and provides support for the hypothesis that alleles harboring 8765delAG are identical by descent in this population. The birthplaces of the grandparents of the mutation carriers were not concentrated in any particular region of Quebec; this is consistent with the families not being closely related. Identity by descent for mutations that are relatively common in the French Canadian population, but rare elsewhere, is expected, since the contemporary population was founded by about 8,500 French migrants who settled in the St. Lawrence valley between 1608 and 1760 [13]. About 3,525 founders who settled in New France before 1680 have been estimated to account for approximately two thirds of the present-day French Canadian gene pool [13,14]. The 8765delAG mutation is probably not common in France, as it was not found among the BRCA2 mutations identified in 16 French breast cancer families [15]. Thus, it is likely that 8765delAG was introduced by one founder, or descendants of one founder, prior to 1680.
Haplotype analysis of three Yemenite Jewish families from Israel using the most distal flanking markers, D13S260 and D13S171, showed that the 8765delAG carriers shared the same alleles [11]. The analysis of additional markers in family BC10 revealed that the diseaseassociated haplotype was 7-3-2-2-T-C-4-6 (table 1). We were unable to establish the disease-associated haplotype for family BC149; however, the genotypes of the carriers in the two Yemenite families are consistent with 8765-delAG being identical by descent.
The BRCA2 8765delAG mutation is a deletion of 2 bp from the sequence AGAGAG. This sequence of three repeats, compared to a longer stretch of repeats, is likely to have a lower mutation rate due to slipped-strand mispairing during DNA replication [16]. However, the presence of three DNA sequence-symmetric elements that include part of the AGAGAG sequence may increase the chance of a deletion of AG. Small deletions in BRCA1 and other genes have been shown to be associated with symmetric elements [17,18].
Our analysis provides evidence that 8765delAG arose independently in the ancestries of the French Canadian and Yemenite Jewish families. Although we cannot rule out an ancient common origin for 8765delAG, we think it less likely, since two recombination events, including an intragenic recombination between the SNPs (or other events), need to have occurred to support the hypothesis of a common origin. During the preparation of this paper, 8765delAG was reported as a founder mutation in hereditary breast cancer families in Sardinia [19]. A comparison of haplotypes from the French Canadian and Sardinian mutation carriers revealed that 8765delAG is associated with different haplotypes in these two populations (data not shown). In conclusion, 8765delAG appears to have arisen independently at least three times, but within the individual populations, it is likely to be identical by descent.